Cisco VPN :: 5520 AnyConnect Can Auth A Machine And Then A User?

We are rolling out a new VPN infrastructure utilizing ASA 5520's (one active/standby cluster at each of our two sites) and making the conversion from the old IPsec client over to AnyConnect 2.5 clients. We do have AnyConnect Premium licenses at both sites, but are not utilizing ISE. What we want to do is first auth the machine that's trying to initiate the AC VPN session to determine if it a company-owned machine (with the idea that only co-owned machines can connect), and then auth the user using RADIUS, which uses attribute 25 to assign them into groups for policy application. We have the RADIUS piece working now, but is there a way to first do the machine auth, and then the user auth? We don't just want to use something like cert-based VPN because if the machine gets stolen (or a non-co user otherwise gets into the OS) then we don't want the non-legit user to be able to establish a VPN session just because they have access to a company machine. The other rub is that the machine auth solution must be cross-OS compatible (we use a mix of Windows, MacOS and Linux on the machines that should be allowed to VPN.)